Weed, as Satch stated it is straight pay, so if it is a five hr trip, you will get paid 75 hrs for the GS and a YS will just tack on the your monthly credit. If you were at 60 before the YS you would not be at 65. A YS does not go above guarantee. A GS does.
So ;
5 hr trip.

YS pays five hrs but is added to credit flown for the month.

GS pay single pay above guarantee for a reserve pilot, so that five hr trip pays a total of 75 hrs, not 80. Line holders get double pay after they hit the regular line holder GS trigger, which is normally about 75 hr or line credit for the month.